Wireless communication method and system for controlling data bit rates to maintain the quality of radio links

ABSTRACT

A wireless communication method and system for controlling the current data bit rate of a radio link (RL) to maintain the quality of the RL. The system includes a core network (CN), a radio network controller (RNC) and at least one wireless transmit/receive unit (WTRU). The RL is established between the RNC and the WTRU. The RNC establishes a guaranteed data bit rate, a maximum data bit rate and a current data bit rate associated with the RL. When the RNC senses an event which indicates that the quality of the RL has substantially deteriorated, the RNC reduces the value of the current data bit rate. Then, in a recovery process, if a similar event does not occur during an established waiting period, the RNC restores the current data bit rate back to the maximum data bit rate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/451,126 filed on Aug. 4, 2014, which is a continuation of U.S. patentapplication Ser. No. 12/170,640, filed Jul. 10, 2008, which issued asU.S. Pat. No. 8,798,009 on Aug. 5, 2014, which is a continuation of U.S.patent application Ser. No. 10/775,629, filed Feb. 10, 2004, whichissued as U.S. Pat. No. 7,408,902 on Aug. 5, 2008 which claims thebenefit of U.S. Provisional Patent Application No. 60/448,233, filedFeb. 13, 2003, the contents of which are hereby incorporated byreference herein.

FIELD OF THE INVENTION

The present invention generally relates to the management of radioresources in a wireless communication system. More particularly, thepresent invention relates to maintaining the quality of a wirelesscommunication radio link (RL).

BACKGROUND

Generally, the RL related aspects of a conventional wireless multi-cellcommunication system are handled by a radio network controller (RNC).Furthermore, the RNC is also responsible for the management of radioresources for the purpose of maintaining RL quality on a per RL basis,otherwise known as link maintenance.

The application of link maintenance applies to both circuit switched andpacket switched services. In the above-mentioned conventional system,the deterioration of radio links occurs due to unpredictablecircumstances. The RL quality of service sometimes falls below anestablished threshold level, or stays below a threshold level for longerthan a predetermined time period.

It is desirable to provide a method and system for adjusting the databit rate of the RL in order to enable efficient link maintenance andavoiding RL quality of service deterioration.

SUMMARY

The present invention is a wireless communication method and system forcontrolling the data bit rate of an RL to maintain the quality of theRL. The system includes a core network (CN), a radio network controller(RNC) and at least one wireless transmit/receive unit (WTRU). The RL isestablished between the RNC and WTRU.

The RNC establishes a guaranteed data bit rate, a maximum data bit rateand a current data bit rate associated with the RL. The RNC senses anevent which indicates that the quality of the RL has substantiallydeteriorated or indicates an inability to maintain the quality of theRL, and determines a target data bit rate based on the sensed event. TheRNC renegotiates a new guaranteed data bit rate with the CN if thetarget data bit rate is less than the guaranteed data bit rate. The RNCreduces the current data bit rate to a target data bit rate byreconfiguration of the Transport Format Combination Set (TFCS). Thisprocess repeats until events, that indicate that the deteriorated RLquality has, ceased to occur.

The sensed event may be the receipt in the RNC of at least onemeasurement indicating that the transmission power is at (or near) amaximum level, or that a block error rate (BLER) associated with theWTRU RL has exceeded a predetermined threshold for a predeterminedperiod of time. The fact that the maximum transmission power has beenreached is either identified by the WTRU for uplink transmissions, or bya Node B for downlink transmissions. The BLER measurement is reported bythe WTRU for downlink transmissions and by Node B for uplinktransmissions.

The RNC may determine the identity of a specific coded compositetransport channel (CCTrCH) associated with the RL. The data bit rate isadjusted by removing one or more Transport Format Combinations (TFCs)from the TFCS associated with the CCTrCH. The process of managing thedata bit rate of each RL operates independently for uplink and downlinkchannels.

In another embodiment, the present invention is a method and system forincreasing the data bit rate following the implementation of acorrective action to maintain the quality of the RL by reducing thecurrent data bit rate from a maximum data bit rate to a reduced data bitrate, or following RL establishment at a data bit rate lower than themaximum data bit rate. The RNC either senses an event that indicates theRL quality has increased beyond a predetermined threshold, or determinesthat an event which indicates that the quality of the RL hassubstantially deteriorated beyond a predetermined threshold does notoccur during a predetermined time period. The RNC then determines theidentity of a specific CCTrCH, associated with the RL, to bereconfigured. The RNC increases the current data bit rate byreconfiguration of the CCTrCH by adding one or more TFCs to a TFCSassociated with the CCTrCH. If the current data bit rate is not equal tothe maximum data bit rate, this process repeats.

BRIEF DESCRIPTION OF THE DRAWING(S)

A more detailed understanding of the invention may be had from thefollowing description of a preferred example, given by way of exampleand to be understood in conjunction with the accompanying drawingswherein:

FIG. 1 is a block diagram of a wireless communication system operatingin accordance with the present invention; and

FIGS. 2A, 2B and 2C, taken together, are a flowchart of a linkmaintenance process used for RL data bit rate reduction and recovery.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a wireless communication method and system forenabling link maintenance to maintain the quality of RLs.

Hereafter, a wireless transmit/receive unit (WTRU) includes but is notlimited to a user equipment, mobile station, fixed or mobile subscriberunit, pager, or any other type of device capable of operating in awireless environment.

The present invention is applicable to communication systems such as auniversal mobile telecommunication system (UMTS), whereby time divisionduplex (TDD), time division multiple access (TDMA), frequency divisionduplex (FDD), code division multiple access (CDMA), CDMA 2000, timedivision synchronous CDMA (TDSCDMA), and orthogonal frequency divisionmultiplexing (OFDM) may be implemented. However, the present inventionis envisaged to be applicable to other types of communication systems aswell.

In third generation (3G) wireless communication systems, possible databit rates and data multiplexing are defined by the available TFCS. EachTFC corresponds to particular data bit rates. By adding and removing atleast one TFC from the TFCS, the maximum possible data bit rate may beincreased or decreased.

FIG. 1 is an exemplary block diagram of a wireless communication system100 operating in accordance with the present invention. System 100includes an RNC 105, a WTRU 110 and a core network (CN) 115. The RNC 105establishes one or more RLs 120A, 120B, with the WTRU 110 to provideuplink and downlink communications. The RNC 105 maintains the RLs 120A,120B, based on the negotiated data bit rates and the desired qualityranges. The RNC 105 and the CN 115 negotiate via path 125 to establish amaximum and a guaranteed, (i.e., minimum), data bit rate for the RLs120A, 120B, such that the quality of the RLs 120A, 120B, remain within adesired quality range having an upper threshold and a lower threshold.

In one embodiment, changes to the data bit rates may be responsive tomeasurement reports received via path 130. The measurement reports mayinclude base station (Node B) and WTRU transmission power measurements,and BLER measurements. The RNC 105 may monitor the measurement reportsto determine when it needs to adjust the current data bit rate tomaintain the quality and maximum data bit rates of the RLs 120A, 120B.

In the event that the link quality falls below an established threshold,if the reported link quality remains below the threshold for apredetermined amount of time, or the system 100 is unable to maintain anacceptable link quality, the RNC 105 reduces the data bit rate of the RL120. Each RL determination of quality and data bit rate adjustments ismanaged independently for the uplink and downlink.

The data bit rate of the RL 120 may be incrementally reduced to afraction of the maximum data bit rate. This is accomplished by removingTFCs from the available TFCS of that CCTrCH. The RNC 105 may reduce thedata bit rate of the RL 120 to as low as the guaranteed data bit ratewithout renegotiating with the CN 115.

If the data bit rate of the RL 120 is already at the guaranteed data bitrate due to a link quality problem, the RNC 105 may attempt torenegotiate the guaranteed data bit rate of the RL 120 via path 125 suchthat the data bit rate of the RLs 120A, 120B, may be further reduced.

After the RL data bit rate is reduced or if the RL 120A, 120B, isestablished at a data bit rate below the maximum data bit rate, then ifeither the RNC 105 senses an event that indicates the quality of RL 120has increased beyond a predetermined threshold or a lower quality ofservice event is not present for a certain period of time, the data bitrate of the RL 120 is incrementally increased. This is accomplished byadding TFCs to the available TFCS of that CCTrCH.

FIGS. 2A, 2B and 2C, taken together, are a flowchart of an RL linkmaintenance process 200 for data bit rate adjustment in accordance withone embodiment of the present invention. During a system steady state,initial RL data bit rate parameters R_(MAX), R_(G) and R_(C) areestablished (step 205), whereby R_(MAX) is the maximum data bit ratepermitted for RLs 120, R_(G) is the guaranteed data bit rate permittedfor RLs 120, and R_(C) is the current data bit rate at which the RLs 120are presently operating. The RNC 105 monitors measurement reportsreceived via path 130 from the WTRU and Node B which indicate thequality level and the ability to maintain the quality level of the RLs120A, 120B. In step 210, a waiting period, (i.e., a predetermined periodof time) is initiated. Based on the BLER and transmission powermeasurement reports 130, the process 200 is capable of sensing when thequality of the RL 120A, 120B, has substantially deteriorated (step 215)and, if so, the data bit rate is reduced by implementing steps 235-260.In step 220, a determination is made as to whether the current data bitrate R_(C) is less than the maximum data bit rate R_(MAX). If R_(C) isless than R_(MAX), the process 200 proceeds to step 225 where it isdetermined whether an event has been sensed that indicates that thequality of the RL 120A, 120B, exceeds a predetermined threshold and, ifso, the data bit rate is increased by implementing steps 265-280. If thepredetermined threshold is not exceeded but, in step 230, the waitingperiod expires without sensing another event indicating a deterioratedquality RL 120A, 120B, the data bit rate is increased by implementingsteps 265-280.

It should be understood that the process 200 for link maintenance isindependently implemented to support uplink and the downlink operations.For the uplink operation, the RNC in step 210 either senses a maximumWTRU transmission power event or high BLER measurement from Node B. Forthe downlink operation, the RNC in step 210 either senses a high BLERreport from the WTRU or maximum (or close to maximum) transmission powerfrom Node B.

The process of reducing the data bit rate is implemented as follows. Instep 235, the specific CCTrCH that will need to be reconfigured isdetermined. In step 240, a new target data bit rate R_(TNEW) isdetermined to correct the sensed RL quality deficiency. If the newtarget data bit rate R_(TNEW) is determined to be greater than or equalto the guaranteed data bit rate R_(G) (step 245), no renegotiation withthe CN 115 is necessary and the current data bit rate R_(C) isdecremented (reduced) until R_(C)=R_(TNEW) (step 255), otherwise the RNC105 renegotiates with the CN 115 via path 125 (step 250). In step 260,the specific CCTrCH determined in step 235 is reconfigured by removingone or more TFCs from the TFCS associated with the CCTrCH. The processthen returns to step 210 where the waiting period begins again.

The process of increasing the data bit rate is implemented as follows.In step 265, the specific CCTrCH that will need to be reconfigured isdetermined. In step 270, a new target data bit rate R_(TNEW) isdetermined that is expected to operate within the predetermined RLquality thresholds. In step 275, the current data bit rate R_(C) isincremented (increased) until R_(C)=R_(TNEW). In step 280, the specificCCTrCH determined in step 265 is reconfigured by adding one or more TFCsto the TFCS associated with the CCTrCH. The process then returns to step210 where the waiting period begins again.

In one embodiment, the number of data bit rate reduction adjustments islimited to a predetermined number. If the number of data bit rateadjustments is exceeded, a handover of the associated RL is implemented.

In another embodiment, if a request to renegotiate the guaranteed databit rate R_(G) with the CN 115 is unsuccessful, (e.g., a waiting periodexpires before the CN 115 provides a response to a data bit rate changerequest), a handover of the associated RL is implemented.

In an alternate embodiment, rather than waiting period expiring withoutany detrimental event being sensed, as in step 230 of process 200, theRNC 105 will instead wait for updated measurements to confirm if thelink quality is back to normal.

If, during the waiting period, the RNC 105 receives a report that thequality of the same RL 120 is too good, (implying the need for data bitrate recovery), the RNC 105 will immediately incrementally increase(recover) the data bit rate of the RL 120. This increase in the data bitrate will not exceed the maximum data bit rate R_(MAX) that wasnegotiated with the CN 115.

When the data bit rate is either reduced or increased, both transportchannel reconfiguration and physical channel reconfiguration may beimplemented for the respective RL. The transport configuration removesand adds TFCs to the TFCS. A physical reconfiguration is used to reduceor increase corresponding physical resources.

While this invention has been particularly shown and described withreference to preferred embodiments, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention describedhereinabove.

What is claimed is:
 1. A wireless network node comprising: a receiverconfigured to receive a first signal from a wireless transmit/receiveunit (WTRU); a processor configured to determine whether a data rate forthe WTRU is to be incrementally increased or incrementally decreased andproduce a second signal to be transmitted to the WTRU so that the WTRUmodifies its transport format combination selection in response to theproduced second signal; and a transmitter configured to transmit thesecond signal to the WTRU.
 2. The wireless network node of claim 1,further comprising: the transmitter further configured to transmit athird signal to the WTRU, wherein the third signal modifies thetransport format combination selection of the WTRU and the third signalis produced based on a determined data rate in response to a negotiatedbit rate with a core network.
 3. A method for use in a wireless networknode, the method comprising: receiving a first signal from a wirelesstransmit/receive unit (WTRU); determining whether a data rate for theWTRU is to be incrementally increased or incrementally decreased andproduce a second signal to be transmitted to the WTRU so that the WTRUmodifies its transport format combination selection in response to theproduced second signal; and transmitting the second signal to the WTRU.4. The method of claim 3, further comprising: transmitting a thirdsignal to the WTRU, wherein the third signal modifies the transportformat combination selection of the WTRU and the third signal isproduced based on a determined data rate in response to a negotiated bitrate with a core network.
 5. A wireless transmit/receive unit (WTRU)comprising: a transmitter configured to transmit a first signal to awireless network node; and a receiver configured to receive a secondsignal from the wireless network node, wherein the second signal isproduced to enable the WTRU to modify its transport format combinationselection and wherein the network node determined whether a data ratefor the WTRU is to be incrementally increased or incrementallydecreased.
 6. The WTRU of claim 5, further comprising: the receiverfurther configured to receive a third signal from the wireless networknode, wherein the third signal modifies the transport format combinationselection of the WTRU and the third signal is produced based on adetermined data rate in response to a negotiated bit rate with a corenetwork.